A flexible synthesis of C33-C39 polyketide region of apratoxin: Synthesis of natural and unnatural analogues

Catalysis Driven Six-Step Synthesis of Apratoxin A Key Polyketide Fragment

Apratoxin A is a potent anticancer natural product whose key polyketide fragment constitutes a considerable challenge for organic synthesis, with five prior syntheses requiring 12 to 20 steps for its preparation. By combining different redox-economical catalytic stereoselective transformations, the key polyketide fragment could be rapidly prepared. Followed by a site-selective protection of the diol, this strategy enables the preparation of the apratoxin A fragment in only six steps, representing the shortest route to this polyketide.

Total synthesis of apratoxin A and B using Matteson's homologation approach

Apratoxin A and B, two members of an interesting class of marine cyclodepsipeptides are synthesized in a straightforward manner via Matteson homologation. Starting from a chiral boronic ester, the polyketide fragment of the apratoxins was obtained via five successive homologation steps in an overall yield of 27% and very good diastereoselectivity. This approach is highly flexible and should allow modification also of this part of the natural products, while previous modifications have been carried out mainly in the peptide fragment.

Evolution of a protecting-group-free total synthesis: studies en route to the neuroactive marine macrolide (-)-palmyrolide A

A full account of our synthetic work toward the first total synthesis of the neuroactive marine macrolide (-)-palmyrolide A is described. Our first-generation approach aimed to unlock the unknown C(5)-C(7) stereochemical relationship via the synthesis of four diastereomers of palmyrolide A aldehyde, a known degradation product. When these efforts provided inconclusive results, recourse to synthesizing all possible stereocombinations of the 15-membered macrolide was undertaken. These studies were critical in confirming the absolute stereochemistry, yielding the first total synthesis of (+)-ent-palmyrolide A. Subsequent to this work, the first protecting-group-free total synthesis of natural (-)-palmyrolide A is also reported.